Easy "Juggler" trophy
Begin Chapter 16, "The Pit" in Graterford, PA. Start in the cafeteria section and collect extra ammunition and Molotov cocktails. Continue until you are attacked in the circular sewer area with waterfalls by leeches and grims. Note: A fully upgraded Rossmore with the flame-thrower secondary upgrade is recommended. Poison, freeze, then burn four grims, in that order simultaneously. To gather four of them together, wait until the second round of attacks in the sewer, when they appear from a waterfall. Shoot a secondary fire cloud from the Mutator at the base of the waterfall where the grims will land. Freeze them while they are upright by switching to your Cryogun. Then, use the Rossmore's secondary flamethrower attack set them on fire.